Method of producing electrical oscillations



Dec. 9, 1941. H. J. R. voN- BA EYER 2,265,784

METHOD OF PRODUCING ELECTRICAL OSCILLATIONS Filed Aug. 31, 1959 OUTPUT ou rpur INVENTOR. HAMS JA/(OB RI? VON BAEYER BY v ATTORNEY.

Patented Dec. 9, 1941 METHOD OF PRODUCING ELECTRICAL OSCILLATIONS Hans Jakob Ritter von Baeyer, Berlin, Germany,

assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphie m. b. H., Berlin, Germany, a

corporation of Germany Application August 31, 1939, Serial No. 292,823

' In Germany September 28, 1938 Claims.

The invention relates to a method of producing electrical oscillations having any desired frequency ranging from the lowest audible frequencies up to the highest ultra high frequencies. It was found many years ago (Righi 1883) that light waves can, under certain conditions, be

brought into interference such that the interfersenses.

able means, such as for instance photoelectric cells, an oscillation generator may be obtainedfor producing any desired frequencies. More especially, this oscillation generator is suited for ultra short waves since the frequency of the luminous oscillations proper is so high that beat frequencies of 10 Hertz and over (corresponding to centimeter waves and millimeter waves) are readily possible. It is presupposed that the light waves which interfere with each other are actually capable of causing such interference, i. e., that they are coherent. The term coherence is employed to denote, in general, that two light waves having the same frequency are constant in time as regards their relative phase position and as regards their relative amplitude which is identical with the requirement that the luminous wave trains emanate from one and the same emission center. This explanation of the coherence, though it is no longer applicable to light waves having different frequencies, can be applied however to the method according to the invention in the manner such that the condition is laid down that the wave trains having different frequencies and whose interference is to be brought about originate from two coherent wave trains having the same frequency, i. e., from one and the same emission center, and that the relative frequency change of the two wave trains was carried subsequently. This condition can, in accordance with a further feature of the invention, be achieved in various ways as will be seen from the accompanying drawing wherein Figs. 1 and 2 illustrate circuit arrangements embodying the principles of the invention.

In one embodiment of the invention, Fig. 1 shows a source of light Q which produces monochromatic light waves, in other words a source, for instance, in the form of the known spectral lamps. This source of light lies in the field of an electromagnet M. The action of the magnetic field of this magnet causes, as is known, the socalled Zeemann effect, i. e., that the original spectral line is split up. in the normal case into two or three spectral lines whereby the central line corresponds with the original line and the outer two lines are the additional new lines. When looking transversely to the magnetic field, all three lines appear and in such manner that the outer two lines are polarized in the same sense while the central line is polarized at right angles to the two outer lines. When looking in the direction of the magnetic field, i. e., when employing magnetic pole shoes which are drilled through, only the outer two lines are visible which in the case are circularly polarized in opposite This splitting up of the original spectral line into two or three lines obvious-1y satisfies the above cited condition of coherence so that fluctuations are produced which can be converted into an intermediate frequency by means of a rectifying organ. Therefore, there is placed in the path of the light waves a photo-cell Z in which the beats resulting from the fluctuations of the luminous intensity are transformed into electrical oscillations. These beats may be derived from the circuit of the photo-electric cell, for instance, by means of the transformer K. Between the photo-cell and the source of light, known Optical means are arranged, more especially a diaphragm B and a lens system L. If the source of light Q is not monochromatic as such, it is necessary to insert between the source of light and the photocell a monochromator since otherwise the entire luminous intensity on the source of light would come primarily from non-displaced lines of the spectrum of the light source so that the actual beats to be observed would become too small in proportion. It is immaterial whether the light waves are derived from the light source at a right angle to the direction of the magnetic field such as shown, or parallel thereto. In the arrangement shown, only the outer two lines interfere with each other since the central line is polarized at right angles thereto. When viewing in the longitudmal direction, the lines which are circularly polarized in opposite senses are to be transformed first into light which is polarized in the linear fashion, for instance by means of a Nicol prism, before the lines impinge the photo-electric cell.

The frequency of the produced oscillations depends entirely on the value of the magnetic field employed so that a gradual frequency change can be obtained by varying the magnetic field, for instance by varying the resistance W in Fig. 1. This signifies an essential advancement over Af=1.4.10 .H

wherein A is the frequency change of the original spectral line expressed in Hertz, and H is the magnetic field in Gauss. If the outer two nous oscillations, v is the speed of the source of light and c is the velocity of light. In accordance with this formula for low beat frequencies only very slow movements of the source of light are required. In the majority of cases it is better to move an image of the light source instead of Y the said source proper, since in this case the atoms proper have no longer an effect.

lines are brought into interference with each other, the beat frequency is obviously equal to twice the frequency change, i. e., equal to 2A It can thus be seen that very high frequencies can 'be attained even at extremely weak magnetic fields and in the case of magnetic fields having the value of 1000 Gauss, which is in practice to be realized, the beat frequency to be expected is already 1.4 and 2.8.10 Hertz which corresponds approximately to a wavelength of 20 centimeters and 10 centimeters, respectively. The amplitude of the produced intermediate frequencies depends on the intensity of the original light source yet it can be easily increased by having the photocell cooperating with the amplifier, or for instance with a secondary emission multiplier of known construction.

The natural width of the line, i. e., the natural frequency band covered by the spectral line need not be considered in the subject matter of the invention since only those components of the split-up spectral lines are capable of interference which satisfy the condition of coherence (in the above stated sense). Consequently, each component of the oscillations is utilized after the splitting-up for the formation of the beat at whatever place of the original spectral line it may be situated and without the components existing in' one and the same line being capable of interference with one another. This corresponds to the known fact that also the normal optical interference phenomena can be provided by broad lines.

' Therehalso exists, as is known,'th'e so-called Stark effect .which is analogous to the Zeemann effect and which signifies the splitting-up of the spectrallines in the electrical field. This effect may likewise be utilized for generating oscillations in the sense of the present invention and in the same manner as is the case with theZeemann effect. Thesplitting-up in thecase of the Stark effect corresponds as to its magnitude approximately to that to the Zeeman effect so that the same frequencies can be expected.

A further effect suited for producing light beats i's'the so-called Doppler eifect of moving luminous'sources. This effect manifests itself in that the frequency of light coming from a source of light moving towards the observer appears increased while when the moving source of light moves away from the observer the said frequency appears decreased. The spectral line of the radiated' lightis shifted, in other words, by the movement of the source of light. Now, when utilizing the original non-shifted line and the shifted line, or the line shifted to the right and the line shifted to the left for producing light beats in the sense of the invention, oscillations having any desired frequency can again be pro-' duced. The value of the Doppler displacementis determined bythe equations wherein-j represents the frequency of the lumi'-' tral apparatus.

Doppler displacements caused by the luminescent For instance, a frosted disc illuminated from the side by any desired light source can be given a uniform speed and the rays may be derived on the one hand in front and on the other hand at the rear of the frosted disc and can be transmitted by means of reflector arrangement to a common photo-cell, so that they interfere with one another on the photo-cell and produce beats. The beat frequency produced corresponds to the difference between the frequency of the spectral lines shifted upwards and the frequency shifted downwards.

In order to realize higher beat frequencies by means of the Doppler effect, preferably luminescent anode rays are employed in which the Doppler effect is as is known of such a magnitude that it can be observed already in sensitive spec- An arrangement suitable in this sense for practising the invention is shown in Fig. 2 in which item B designates a tube for anode rays having essentially an anode A and a perforated cathode K and which is filled with a rarefied gas or with a metal vapor. The luminescent anode ray is observed through two observation tubes B1 and B2 in two directions extending in the opposite senses so that the reflector S1v isimpinged by the spectral line which is shifted towards higher frequencies while the reflector S2 is impinged by the spectral line which is shifted towards lower frequencies. Both light wave trains are brought into interference by means of suitable reflector arrangements and are conducted to a photo-electric cell.

. ment there is also to be taken into consideration the angle between the direction of observation and the direction of the anode rays since it is only the component of the movement of the light source measured in the. direction of viewing which as is obvious figures in the Doppler effect.

As regards themonochromatic properties of the source of light, the same conditions exist also when employing the Doppler effect; Therefore,

if necessary, additional monochromators are to be used. Furthermore, the anode ray tube mayhave special means to render homogeneous the velocity of the anode rays. I

In the examples of construction according to the invention which so far have been describedherein, the simplifying presupposition was made that the two trains of light wavesto be-brought intoin-terference extend strictly parallel toeach "other. In this case the interference pi-cture' is constant at all places in space so that the observation can be carried out with a photocell of any desired dimensions. But if the two light Wave trains form 'a small angle with'each other such 1 as is usually the case in the ordinary interference tests in the optical field; therewill be ob-- tamed these-called interference picture with-al- In this arrangeternating maxima and minima of the light intensity. But contrary to the ordinary optical interference tests with wave trains of light of the same frequency, the interference picture does not remain stationary in space but wanders at a speed of travel which corresponds to the frequency difference between the two wave trains of light. Now, when placing in the path of the rays a photo-cell whose dimensions are comparable with or small against the distance between two interference stripes, the maxima and minima move past this photo-cell causing thereby electrical oscillations in the same manner as above explained.

Finally, it should be pointed out that outer means are not at all necessary for the production of light beats which means cause a coherent frequency shift. Instead, in many cases adjacent spectral lines may already be present in the source of light proper which comply with the conditions of coherence and can thus be utilized in the sense of the invention for the formation of beats. This is true more especially in electric discharge tubes in which the magnetic field of the discharge proper and furthermore the magnetic earth field result in a splitting up of the line through the Zeemann effect.

The present invention is not limited to the examples of construction herein given and permits of any desired structural possibilities. Thus the photo-cell serving for transforming the beats of the light into electrical oscillations may be directly a part of a dipole which in this way will be energized to furnish high-frequency oscillations. Furthermore, it is possible to modulate the produced oscillations by influencing the intensity of the light and more especially a frequency modulation is possible by influencing the splitting-up of the lines, i. e., by a change of the magnetic field in the case of the Zeemann eifect, or by a change of the potential at the anode ray tube.

What is claimed is:

1. The method of producing electrical oscillations which includes the steps of splitting a ray of monochromatic light into components having different frequenciesfcausing said components to interfere with each other, and converting their resultant into a unidirectional electric current whose average value is proportional to the vector sum of the two components and whose frequency of variation is equal to the frequency difference of said two components.

2. In a system for the production of waves of the order of a few centimeters and less, a source of monochromatic light energy, means for effectively modulating said light energy at a frequency relatively low compared to said light frequency and corresponding to the desired frequency to be obtained, nonlinear means for converting said modulated light into varying unidirectional electric current, and means for selecting from said current the component of frequency corresponding to the desired frequency.

3. In a system for the production of ultra short waves, a source of monochromatic light, a magnet for splitting up a ray of light from said source into components having different frequencies, a photoelectric cell upon which said components impinge for translating said components into electric current, a diaphragm and a lens located between said source and said cell and in the path of said rays, and a transformer having one winding connected between the electrodes of said cell and another winding connected to an output circuit.

4. In a system for the production of ultra short waves, a gaseous discharge device having within an envelope an anode at one end of the envelope and a perforated cathode intermediate the ends, a pair of hollow observation tubes connected to said envelope and located on the side of said cathode removed from said anode, means for obtaining from said tubes components of light having different frequencies, non-linear electric means in the paths of travel of said components for translating said components into electric current which varies at a frequency corresponding to the difference of the frequencies of said components.

5. The method of producing electrical oscillations which comprises the steps of splitting a monochromatic light beam into components having different frequencies by means of a constant magnetic field, and translating the total light flux of said components non-linearly into electric current.

6. The method of producing electrical oscillations which includes the steps of producing two beams of monochromatic light having components of different frequencies, causing said components to interfere with each other, and converting their resultant into a unidirectional electric current Whose average value is proportional to the vector sum of the two components and Whose frequency of variation is equal to the frequency difference of said two components.

7. In a system for the production of ultra short waves, a source of monochromatic light, a magnet for splitting up a ray of light from said source into components having different frequencies, a photoelectric cell upon which said components impinge for translating said components into electric current, and an output circuit for utilizing the variations in said electric current.

8. In a system for the production of ultra short waves, an electric tube having therein a moving source of monochromatic light, means for obtaining from said moving source two rays of light along different directions such that the component of source velocity along said directions is different, a photo-cell and means for bringing said two rays together onto said photocell, and an output circuit coupled to said photocell.

9. In a system for the production of ultra short waves, a source of light, means for producing from said source components of monochromatic light having different frequencies including an element for producing a constant magnetic field, a rectifying element upon which said components impinge for translating said components into electric current, and an output circuit for utilizing the variations in said electric current.

10. In a system for the production of ultra short waves, a monochromatic source of light, means for frequency modulating said light to produce a plurality of frequency components, and a rectifier for producing from the resultant of said components a unidirectional current of intensity which Varies in accordance with the modulation.

HANS J AKOB BITTER VON BAEYER. 

